img2pdf is a simple commandline utility to convert a list of PNG, TIFF, or JPEG images to a single PDF document, one image per page. It was designed specifically to convert scanned pages to PDF format, but it will accept images of any aspect ratio and scale them to full page size (which, in general, will not maintain the aspect ratio). The hard work is performed by the Panda PDF library and its dependencies.

OptiPNG is a PNG optimizer that recompresses the image files to a smaller size without losing any data. It works in a manner similar to pngcrush, but it has a wider automatic search space (leading to possibly a better compression), and it runs faster.

ObjectPlanet's PngEncoder is a fast PNG encoder. The footprint is just
over 5K, and the internal object creation during runtime is kept to a
minimum to avoid calls to the garbage collector. It is compatible with
JDK 1.1 and later.

Tumble converts one or more TIFF (B&W only) and
JPEG files into a PDF file. It was developed
primarily for use with scanned images. B&W images
will be encoded with Group 4 fax (T.6) lossless
compression. JPEG images are embedded as-is.
Tumble supports multi-page TIFF files, and can
generate PDF outline entries (bookmarks) based on
the file name and/or the page number.

GraphicsMagick is a robust collection of tools and libraries which support reading, writing, and manipulating an image in over 90 major formats including popular formats like DPX, DICOM, BMP, GIF, JPEG, JPEG-2000, PDF, PNG, PNM, SVG, and TIFF. A high-quality 2D renderer is included, which provides a subset of SVG capabilities. C, C++, Perl, Tcl, and Ruby are supported. Originally based on ImageMagick, GraphicsMagick focuses on performance, minimizing bugs, and providing stable APIs and ABIs. It runs on all modern variants of Unix, Windows, and Mac OS X.

IsaViz is a visual environment for browsing and authoring Resource Description Framework (RDF) models represented as graphs. It features a 2.5D user interface allowing smooth zooming and navigation in the graph; creation and editing of graphs by drawing ellipses, boxes, and arcs; RDF/XML, Notation 3 and N-Triple export; and also SVG and PNG export.